Polyimides represent an important class of hightemperature polymers with a broad range of applications. In the electronics industry, they are used in many applications which take advantage of their thermal stability, good electrical properties and other very useful characteristics. Polyimides, however, tend to absorb moisture, which results in changes in electrical properties under varied humidity conditions. Additionally, as the drive in electronics for smaller size continues, materials with improved dielectric properties, e.g., lower dielectric constant, are required.
Fluorination has been used to reduce both moisture absorption and dielectric constant in polyimides. For example, Japanese Patent Application Publication (Kokai) No. 1-190652 (Appl. No. 63-12660), Japanese Patent Application Publication (Kokai) No. Hei 2-60933 (Appl. No. 63-211799), and Japanese Patent Application Publication (Kokai) No. Hei 1-18860 (Appl. No. 63-4760) disclose use of perfluoroalkyldiaminobenzene in preparing polyimides. However, the raw materials for preparing such diamines are not readily available, and thus, it is not easy to prepare these compounds, especially in pure state without the presence of undesirable homologues. Another disadvantage of these compounds is that their reactivity is very low, due to the electron withdrawing power of the pendant perfluorinated group, which is directly connected to the benzene ring. Removal of the direct connection of the perfluorinated group from the benzene ring through the introduction of one or more intermediate methylene groups is undesirable, since the thermal stability degrades due to premature dehydrofluorination.
In contrast, the perfluorinated alkyl group, according to the present invention, is connected to the benzene ring through a tertiary carbon atom followed by a methylene group. Due to the absence of hydrogen on the carbon atom adjacent to the fluorinated carbon atoms, no dehydrofluorination takes place.